The invention disclosed broadly relates to the field of hard disk drives, and more particularly, relates to the field of actuators for hard disk drives.
Hard disk drive storage typically uses a multitude of rotating rigid disks for storage of data on a magnetic thin film on the disk surfaces. The stored data is written to or read from these disks by using transducer heads that are driven, by an actuator system, in a path towards and away from the center of the disks. The data is recorded in concentric circumferential tracks arrayed on the surfaces of the disks.
Today nearly all actuators, for positioning the transducer heads relative to the disk surfaces, are of the rotary variety. These rotary actuators typically include a pivotable support member and a comb assembly comprising of several closely spaced rigid arms. At least one transducer head is attached to each rigid arm. Typically, this comb assembly includes an extension, opposite in direction to the rigid arms, which is driven in a pivotal motion by a voice coil motor. The voice coil, cooperating with permanent magnets and the core assembly, is operatively controlled for moving the transducer heads in synchronism in a radial direction in order to position the heads with the data tracks to be followed.
As information storage devices having smaller physical sizes and larger storage capacity are required for information processing systems, there is a need for rotary actuator motors having more torque but consuming less power. The traditional approach is to use more powerful voice coil motors in the smaller sized designs. However, along with the increase in power there is a corresponding penalty in high bandwidth performance. This is due to a worsening of the bending modes of the actuator system. One approach to solving this problem is the use of a balanced mode of actuation. A rotary actuator utilizing a balanced configuration is discussed in U.S. Pat. No. 5,267,110 issued to Ottesen, et al.
One of the bending modes of the actuator system is the butterfly mode of bending for the main voice coil motor (VCM). It is a major limiting factor in achieving higher bandwidth servo for higher track densities. This butterfly mode has a 180 degree phase shift associated with it which is difficult to compensate by any electronic or filtering means. By the incorporation of a balanced configuration for the voice coil motor, used to perform the high bandwidth track following, one can sidestep the butterfly mode and associated phase shift of the typical VCM. The linear force that excites this butterfly mode is virtually eliminated in a balanced configuration.
A recent actuator motor design is disclosed in a co-pending patent application that is assigned to the assignee of the instant application. This application is titled xe2x80x9cDisk Drive with a Pivot Embedded Torque Generating Track Following Actuator and Method Therefor,xe2x80x9d U.S. Ser. No. 09/877,012, and is hereby incorporated by reference herein. In this co-pending application is disclosed the use of a typical VCM motor to provide the high powered seek movement and the use of a balanced micro-VCM to provide the high bandwidth track following. The micro-VCM is embedded in the pivot of the actuator system.
Briefly, according to the invention, a micro-VCM motor for incorporation in an actuator pivot comprises (includes but is not limited to) a motor shaft, a coil disk, an upper magnet-yoke disk, a lower magnet-yoke disk and a motor housing. The coil disk is attached to the shaft to form a shaft-coil assembly.
The coil disk comprises two or more (a plurality of) coils. Each coil is placed orthogonally (perpendicular) to the axis of the shaft. One-half of the coils are configured to receive an electrical current in a first direction. The other half of the coils are each configured to receive a second electrical current in a second direction so that all the coils generate a torque in the same direction but with a net resultant linear force being substantially equal to zero. Each of the other half of the coils is located diametrically opposite to one of the coils receiving current in the opposite direction.
The upper magnet-yoke disk is mounted relative to the shaft at a location above the coil disk so that it rotates with respect to the coil disk. The upper magnet-yoke ring comprises at least one magnet, aligned in a first direction, and a respective number of yokes. Each yoke holds a magnet such that magnetic lines of flux are generated parallel to the motor shaft axis.
The lower magnet-yoke disk is mounted relative to the shaft at a location below the coil disk so that it rotates with respect to the coil disk. The lower magnet-yoke disk comprises at least one magnet aligned in a direction opposite from the direction of the magnet(s) of the upper magnet-coil disk, and a respective number of yokes to hold the magnet(s).
The upper and lower magnet-yoke disks are both fixed to a motor housing (outer sleeve) such that all three comprise the rotating part of the actuator pivot motor. The actuator comb assembly is, in turn, attached to this rotating part of the motor and will pivotally rotate with the same.